This invention relates to a process for producing a graft copolymer by reacting an ethylenically unsaturated monomer with a fluorine-containing resin.
Recently, from the viewpoint of saving resources and saving energy, there have strongly been desired coating compositions excellent in weather resistance, that is, providing maintenance-free coating film even in paint industry. Heretofore, acrylic resins have been used in fields wherein weather resistance is required, but a further improvement is required now.
Further, the acrylic resins have defects in that they are generally poor in drape with pigments having higher oil absorbing properties, particularly they are remarkably poor in pigment dispersion as to carbon black and the like pigments, they require a longer time to obtain uniform dispersion, they cause pigment separation during storage, and the like. In order to improve the pigment dispersibility, it is proposed to synthesize an acrylic resin in the presense of an alkyd resin having unsaturated carbon-carbon double bonds. The resulting resin is improved in the pigment dispersibility but inferior in weather resistance and chemical resistance to the acrylic resins before modified.
On the other hand, there are known fluorine-containing copolymers having as essential components fluoroolefin, hydroxyalkyl vinyl ether, alkyl vinyl ether and cyclohexyl vinyl ether. These fluorine-containing copolymers are excellent in weather resistance, but poor in pigment dispersibility and initial gloss. In order to improve such defects, it is proposed to produce a graft copolymer by polymerizing an ethylenically unsaturated monomer in the presence of a fluorine-containing copolymer mentioned above to which reactive carbon-carbon double bonds were introduced (Japanese Patent Unexamined Publication No. 59-41315). The resulting graft copolymer is excellent in the weather resistance, pigment dispersibility and initial gloss, but has defects in that it is insufficient in compatibility with the ethylenically unsaturated monomer and its polymer, the graft copolymer solution is often clouded, the pigment can disperse but is easily separated from the resin component, and the like.